Under the units of production method, the amount of depreciation charged to expense varies in direct proportion to the amount of asset usage. Thus, a business may charge more depreciation in periods when there is more asset usage, and less depreciation in periods when there is less usage. It is the most accurate method for charging depreciation, since this method links closely to the wear and tear on assets. However, it also requires that someone track asset usage, which means that its use is generally limited to more expensive assets. Also, you need to be able to estimate total usage over the life of the asset in order to derive the amount of depreciation to recognize in each accounting period.
If the estimated number of hours of usage or units of production changes over time, incorporate these changes into the calculation of the depreciation cost per hour or unit of production. This will alter the depreciation expense on a go-forward basis. A change in the estimate does not impact depreciation that has already been recognized.
Machine hour rate is useful for calculating the value of different overheads fastly. Because depreciation is one of main overhead of the business, so, we can use machine hour rate method for calculating the value of depreciation.
As per machine hour rate method of depreciation, we calculate the total life of any fixed asset on the basis of its working hours life. After this, we divide actual cost of fixed assets with life of fixed assets in hours. After dividing, we will obtain the depreciation rate per hour. This method will apply mostly on the machines. So, in following formula, we have used the word machine instead of fixed asset. You can also find any other fixed asset's hourly depreciation rate with following formula by changing the cost of machine, scrap value and estimated life in hours.